(1) Field of the Invention
The present invention relates to a display device, and in particular, to a technology for connecting IC drivers to wires of which the pitch has become smaller as the display devices are miniaturized, the definition of the screens increases, and the IC drivers are miniaturized.
(2) Description of the Related Art
Liquid crystal display devices are formed such that pixel electrodes and thin film transistors (TFT's) are formed in a matrix on a TFT substrate to which a facing substrate, where color filters are formed in locations corresponding to the pixel electrodes, is attached so that liquid crystal is sandwiched between the TFT substrate and the facing substrate. Thus, the transmittance of light is controlled for each pixel by the liquid crystal molecules so that an image is formed.
A number of video signal lines running in the longitudinal direction and aligned in the lateral direction and a number of scan signal lines running in the lateral direction and aligned in the longitudinal direction are formed on a TFT substrate, and pixels are formed in the regions surrounded by the video signal lines and the scan signal lines. Each pixel is mainly formed of a pixel electrode and a thin film transistor (TFT, which is a switching element). Thus, a great number of pixels formed in a matrix form a display region. TFT's are formed in the display region on the TFT substrate, and an inorganic passivation film is formed on top and pixel electrodes are formed on top on this. An insulating film, such as of SiN, is formed as the inorganic passivation film, and a transparent conductive film, such as of ITO (indium tin oxide), is used for the pixel electrodes.
A terminal group for supplying signals (video signals) to video signal lines and a terminal group for supplying signals (scan signals) to scan signal lines are formed around the outside of the display region on the TFT substrate. In addition, IC drivers (driver chips) bumps are connected to these terminal groups. Here, as the definition of the screen increases, the number of terminals connected to the IC drivers increases and the pitch between terminals decreases. In addition, decrease in the pitch between bumps as the IC drivers are miniaturized also becomes a factor that makes the pitch between terminals decrease. Thus, the area through which bumps formed on the IC drives and terminals are connected cannot be secured sufficiently. JP2008-020791A describes the configuration where the pitch between wires is smaller than the pitch between the bumps on the IC drivers, and the wires and the bumps are connected in several staggered places so that the pitch between the bumps and the pitch between the wires match.
In the case where the display device is miniaturized and the frame around the display region becomes smaller, a structure where lead lines for scan signal lines, in particular, are collected along one side of the display device is adopted. In this case, a large area is required for all of the above described lead lines to be wired on one surface. In order to avoid this, the above described lead lines are wired three-dimensionally (in multiple layers) via insulating films in between so that the area for wiring can be reduced. Such a structure is described in JP2004-53702A, for example.
In addition, wires formed in display devices are inspected to see whether or not there is a short circuit at a stage before mounting IC drivers during the manufacturing process for a display device. In the case where a defect, such as short-circuiting of a wire, is discovered at this stage, it is not necessary to carry out the subsequent steps on the defective display device, and thus, the cost for manufacture can be reduced. In this case, the TFT switches driven at the time of inspection are formed in the region where IC drivers are to be mounted, that is to say, in the region that is to be hidden by the IC drivers mounted afterwards. JP2008-9246A describes a structure of a display device that makes this inspection step possible.